Such transmissions or rather drive units are among others utilized in industrial trucks as for example forklifts. A use is known from a Carl Hurth Maschinenund Zahnradfabrik GmbH & Co. (a/k/a/ HURTH Getriebe und Zahnraeder G.m.b.H.) reference entitled "HURTH Getriebe fuer Flurfoerderzeuge Baureihe HFS" (Hurth Drive Units for Industrial Trucks HFS Line) dated February, 1988, where such use is illustrated in a significantly simplified manner in FIG. 1 of the drawings accompanying this text. Two drive units 4, 5 are arranged in a mirror-image fashion to one another to function as a double drive mounted on side frame members 1, 2 of a front-drive industrial truck (not illustrated in detail), which side frame members are connected to each other through transversely extending bars 3. Each drive unit consists of a spur gear transmission 7, to which an electric motor 6 is connected and on the driven shaft of which, which is constructed as a wheel shaft 8, is mounted a drive wheel 9. A combination wheel and blocking brake 10 is provided on the sides of each of the electric motors 6 remote from the transmissions 7. FIG. 1 clearly permits one to recognize that the brakes 10 take up almost all the space (distance a) remaining between the motors 6 so that neither larger, namely, in particular longer, electric motors can be used nor is a reduction in the frame width b possible.
Therefore, the basic purpose of the invention is to provide a drive unit of the above-mentioned type such that, while reducing the space a existing up to now between the electric motors 6, larger, namely, longer electric motors with higher performance can be installed and/or the frame width b can be reduced, which up to now was prevented by the existing arrangement of the brakes 10.
This purpose is attained according to the invention by the brakes being integrated into the transmissions.
A brake also integrated in a drive unit for an industrial truck, which brake is operated from outside by a bent double lever, is known from DE 23 57 451 C2, however, the known brake cannot be utilized in the present case: On the one hand, the operating levers passing by on the outside of the drive wheels would further increase the total width of the drive unit, and on the other hand, no structural part, to which the operating levers could be hinged, exists above or in front of or behind the drive wheels 9.
The spur gear transmissions for the mentioned use must as a rule be designed in two steps in order to be able to house the necessary translation. Particularly advantageous is thereby that the axial distance between the spur gears of the first step and the planetary gear set of the second step must not be enlarged compared with the known design. This means that the brake integrated into the transmission does not require any additional space.
The disk brake known from the above-mentioned DE 23 57 451 C2 can only be operated mechanically. A hydraulic operation is not possible here since in transmissions for industrial trucks the space needed for cylinders, pistons, seals, etc. is usually not available.
A further development of the invention includes the provision of a disk brake of the mentioned type, in which a hydraulic operation is possible without requiring additional space inside the transmission housing. The integration of the hydraulic cylinder into the operating lever thereby brings about several surprising advantages: A very small cylinder diameter is possible due to the leveraging capability of the operating lever, the transmission oil within the transmission housing and the brake fluid are spacially completely separated from one another without expensive and complicated seals, and the lever with the hydraulic cylinder thereon, which is to be viewed as a wear part, can be exchanged in a service-friendly manner--without having to remove the transmission from the truck and without having to disassemble the transmission.